i think that is a good thing to keep track off the figured compresion from the top off exhboster ports to top deadccenter volume ..........but i think in a two stroke that the rpm and the diamter of the exh pipe stinger and cone giong into the stingers vary the amount of pressure that is created in the cylinder ..so these cylinder head ccs and compresion numbers become refrence numbers ,, and we can find combos that work very well or not with a given fuel timing or pipe..so it helpful to look at sevral comprsion figures in a given moter,,